BROWNSVILLE, Texas (ValleyCentral) — The Gladys Porter Zoo announced Wednesday the passing of one of their gorillas.

Penney, 36, passed away on May 19 of suspected cardio-respiratory failure.

According to the GPZ, Penney was looking “less robust than normal,” resulting zoo-keepers to conduct a full-diagnostic evaluation on her.

The day before her passing, Penney was anesthetized, blood was drawn, an EKG was conducted, X-rays were taken and urine/stool samples were collected.

Although the samples did not raise any red flags, GPZ staff members kept watch over Penney over night after her workup evaluation.

In the morning, she didn’t wake up from her sleep and died shortly after, GPZ stated.

The zoo determined that Penney had fluid around her heart and that she may have died from cardio-respiratory failure and secondary renal failure.

“Her left ventricle was firm and constricted,” a press release from the Gladys Porter Zoo stated. “In addition, there seemed to be a loss of structural detail in her left kidney.”

Tissue samples have been sent out for a complete histopathology to determine what caused the rapid decline in her health.